1. Field of the Invention
This invention relates to methods, devices, and systems for making and controlling connections to industrial pressure vessels. In one example, the invention relates to a removable insert for valve manifold that connects to pressure vessel. Another example relates to a valve manifold that applies pressure to a closing portion of a valve so as to assist in closing the valve against a seat. Another example relates to a manifold connection that reduces or prevents dimensional changes in a portion of a pressure vessel or a part connected to a pressure vessel from transmitting force or moment to a nozzle connection. In certain examples, the above-noted arrangements relate to use in pressure swing adsorption (PSA) apparatuses.
2. Description of the Related Art
Early PSA systems generally used four adsorbent vessels operated in parallel. An example of such a PSA system is described in U.S. Pat. No. 3,430,418 to Wagner. Later improvements to Wagner's process added an additional pressure equalization step while retaining four adsorbent beds (see U.S. Pat. No. 3,564,816 to Batta), and subsequently added even more pressure equalization steps to seven or more beds (see U.S. Pat. No. 3,986,849 to Fuderer et al.). These increases in the number of pressure equalizations and the number of adsorbent vessels were implemented to increase the product recovery and the adsorbent productivity. The increases in performance were also typically accompanied by a coincident increase in the number of valves required to operate the systems. For example, the Wagner system utilized at least thirty-one valves, the Batta system utilized at least thirty-three valves, and the Fuderer et al. system utilized at least forty-four valves.
Some PSA systems are often single point of failure systems, with notable exceptions being the processes revealed in U.S. Pat. No. 4,234,322 to De Meyer et al. and U.S. Pat. No. 6,699,307 to Lomax Jr., the entire contents of each of which are incorporated herein by reference. Even in the above-noted processes, the PSA plant is typically shutdown to conduct maintenance on the defective component. Such shutdowns are undesirable as they can cause lost production time for the entire process facility.
A pressure swing adsorption system that can be repaired while in operation was proposed by U.S. Pat. No. 6,918,953, to Lomax Jr et al., the entire content of which is incorporated herein by reference. This system addresses the shutdown concern by implementing PSA modules which provide redundant operation allowing for single modules to be taken offline for maintenance without taking the entire PSA system offline. Each module includes a top and bottom manifold that contains internal flow passages for communication between the feed, product, raffinate, and equalization flow between each vessel in the manifold. One example of another PSA module is described in U.S. Pat. No. 6,755,895 to Lomax Jr. et al., the entire contents of which are hereby incorporated by reference.
While the modular PSA design reduces the single point of failure nature of the conventional PSA design, it still has a large number of moving parts which may require maintenance.
PSA valves typically cycle frequently, and as a result, these valves may incur wear which can potentially lead to a leak in a valve. Internal leaks occur when the seat or valve member (also referred to as the disc) is damaged resulting in a pathway for gas to flow between the two. This can affect the purity of the PSA separation thus any leaking valve needs to be repaired quickly.
As shown in FIG. 12, a conventional pressure swing absorption apparatus is shown with a pressure vessel and a manifold connected to the pressure vessel. The manifold is connected to the pressure vessel via a rigid connection. In this background figure, the rigid connection is via threading on a neck that protrudes from a bottom plate connected to the pressure vessel. The neck places a plenum cavity in the valve manifold in fluid communication with a nozzle disposed within the pressure vessel. Thus, gas flowing from the adsorptive material can pass into the plenum cavity via the nozzle, and gas within the plenum cavity can pass within the pressure vessel in order to contact the adsorptive material inside. Passages connect the plenum cavity to channels. The passages can be opened or closed via valves disposed in ports in the valve manifold. The above-noted arrangement provides certain benefits inasmuch as the valve manifold reduces the total number of plumbing connections that have to be made in order to correctly plumb a pressure swing absorption system. This reduction in plumbing reduces the weight of the system, reduces the cost of the system, and increases the reliability of the system.
However, certain disadvantages occur with the system described in FIG. 12. For example, the rigid connection between the pressure vessel and the valve manifold can result in transfer of stress from the pressure vessel to the valve manifold when the pressure vessel is pressurized. In other words, when the pressure vessel is pressurized, the plate, and therefore the neck on the bottom of the plate, will tend to displace in a direction toward the valve manifold. In some cases, the displacement can be as much as 0.20 inches. This displacement can cause stress to connections made to the valve manifold. In certain cases, leaks or cracks may occur in the plumbing connected to the valve manifold as a result of the displacement caused by the pressure inside the pressure vessel.
Additionally, as shown in FIG. 12, the valves are connected directly to the valve manifold, and the seal of the valve, for example, a gasket, will seat on a valve seat disposed on the valve manifold itself. One potential problem with the above-noted arrangement is that the valve seat, which is part of the valve manifold, is difficult to rework or service if it should become scratched or otherwise marred. In some cases, if the valve seat is extensively damaged, the entire valve manifold will have to be replaced merely because the valve seat leaks.
Another potential disadvantage to the system described in FIG. 12 is that the valves are preferably biased to a normally closed position. In other words, absent other factors, the valves will default to seal the passage between the plenum cavity and the channels. This preference is due in part to safety concerns. In some instances, the pressure inside the plenum cavity is higher than the pressure inside the channels. For many valve manifolds, the bias in the valves is created by a biasing device such as a spring. When the overall open area of the passage is relatively small, the surface area of the seal assembly portion of the valve exposed to pressure is also relatively small, and the biasing mechanism, e.g., spring, is sufficiently strong to overcome the pressure applied to the bottom of the valve. In this case the valve will remain closed due to the biasing force produced by the biasing device. However, in sufficiently large valve manifolds, the passages become so large that it is difficult or prohibitively complicated to provide a biasing mechanism that will maintain the valve in a closed state when the pressure inside the plenum cavity is larger than the pressure inside the channel.